Vehicles such as automobiles have become increasingly sophisticated, with a large number of computer controlled and monitored sensors, switches, motors and lamps. Electrical wiring harnesses in automobiles were complex and expensive components requiring a great deal of space and labor to install, even before the shift to computerization. Wiring harnesses are also a common point of failure that are notoriously difficult to diagnose and repair because of their complexity and their placement in inaccessible and tightly packed locations. The environment in which the wiring harnesses are placed is extremely inhospitable, with wide temperature variations, constant physical movement and shock when the automobile is in motion, and the exposure to dust and grime and even to moisture in the case of leaks and spills.
One common way to minimize the number of wires in a wiring harness is to connect components with a bus in a network rather than dedicating one or more wires to each component. A local interconnect network (LIN) is a bus-based network originally developed for use in automobiles, but that may be used in other applications. The LIN is generally a single wire serial broadcast network having one master and multiple slave devices. The LIN does not support collision detection, so communication on the bus is initiated only by the master device, although the slave devices may communicate directly between themselves after the master initiates a message. In addition to reducing the number of wires in wiring harnesses, the LIN includes error detection to ensure that data is transmitted correctly. Data may be transmitted and received using a universal asynchronous receiver-transmitter (UART) either included in a microcontroller or in dedicated LIN hardware or in custom integrated circuits.
A LIN is a relatively slow and low-cost network primarily used in difficult environments such as automobiles which often generate a great deal of electromagnetic interference (EMI). Thus, LIN transceivers have strict EMI performance requirements enabling them to function properly in the presence of substantial interference. The EMI performance is tested in a direct power injection (DPI) test in which high power at a wide range of frequencies is injected onto a single LIN node or pin such as the output of a LIN driver. This results in coupling to various sensitive internal nodes in the LIN driver circuit and reduces the transmission performance. The coupling from the DPI at the LIN driver output to other nodes in the system must be limited to a specified level, such as 34 dBm (decibels of measured power referenced to one milliwatt) without a capacitor on the LIN driver output or 36 dBm with a capacitor. It is difficult to achieve this level of EMI performance in a LIN using conventional driver topologies.